Photodiode and photodiode array

ABSTRACT

A photodiode array PDA 1  is provided with a substrate S wherein a plurality of photodetecting channels CH have an n-type semiconductor layer  32 . The photodiode array PDA 1  is provided with a p −  type semiconductor layer  33  formed on the n-type semiconductor layer  32 , resistors  24  provided for the respective photodetecting channels CH and each having one end portion connected to a signal conducting wire  23 , and an n-type separating portion  40  formed between the plurality of photodetecting channels CH. The p −  type semiconductor layer  33  forms pn junctions at an interface to the n-type semiconductor layer  32  and has a plurality of multiplication regions AM for avalanche multiplication of carriers generated with incidence of detection target light, corresponding to the respective photodetecting channels. An irregular asperity  10  is formed in a surface of the n-type semiconductor layer  32  and the surface is optically exposed.

TECHNICAL FIELD

The present invention relates to a photodiode and a photodiode array.

BACKGROUND ART

A photodiode using compound semiconductors is known as a photodiode witha high spectral sensitivity characteristic in the near-infraredwavelength band (e.g., cf. Patent Literature 1). The photodiodedescribed in Patent Literature 1 is provided with a first lightreceiving layer comprised of one of InGaAsN, InGaAsNSb, and InGaAsNP,and a second light receiving layer having an absorption edge at a longerwavelength than that of the first light receiving layer and comprised ofa quantum well structure.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-open No.    2008-153311

SUMMARY OF INVENTION Technical Problem

However, such photodiodes using the compound semiconductors are stillexpensive and their manufacturing steps are also complicated. For thisreason, there are desires for practical application of a siliconphotodiode being inexpensive and easy to manufacture and havingsufficient spectral sensitivity in the near-infrared wavelength band.The conventional silicon photodiodes generally had the spectralsensitivity characteristic with the limit of about 1100 nm on the longwavelength side, but the spectral sensitivity characteristic in thewavelength band of not less than 1000 nm was not enough.

It is an object of the present invention to provide a silicon photodiodeand a silicon photodiode array as a photodiode and a photodiode arrayhaving a sufficient spectral sensitivity characteristic in thenear-infrared wavelength band.

Solution to Problem

A photodiode array according to the present invention is a photodiodearray in which a plurality of photodetecting channels for detectiontarget light to be entered thereinto are formed on a silicon substratehaving a semiconductor layer of a first conductivity type, thephotodiode array comprising: an epitaxial semiconductor layer of asecond conductivity type formed on the semiconductor layer of the firstconductivity type, forming pn junctions at an interface to thesemiconductor layer, and having a plurality of multiplication regionsfor avalanche multiplication of carriers generated with incidence of thedetection target light, so that the multiplication regions correspond tothe respective photodetecting channels; and a plurality of resistorseach having two end portions, provided for the respective photodetectingchannels, and each electrically connected through one of the endportions to the epitaxial semiconductor layer and connected through theother of the end portions to a signal conducting wire, wherein anirregular asperity is formed in at least a surface corresponding to thephotodetecting channels in the semiconductor layer of the firstconductivity type, and wherein at least the surface corresponding to thephotodetecting channels in the semiconductor layer of the firstconductivity type is optically exposed.

In the photodiode array according to the present invention, the pnjunctions are composed of the semiconductor layer of the firstconductivity type and the epitaxial semiconductor layer formed on thesemiconductor layer. The multiplication regions are formed in theepitaxial semiconductor layer where the pn junctions aresubstantialized, and the multiplication regions corresponding to therespective photodetecting channels are present in this epitaxialsemiconductor layer. Therefore, the photodiode array has no end portions(edges) of the pn junctions to cause edge breakdown when operated in aGeiger mode, and thus there is no need for providing a guard ring. Forthis reason, the photodiode array can have a higher aperture rate.

In the present invention, the irregular asperity is formed in at leastthe surface corresponding to the photodetecting channels in thesemiconductor layer of the first conductivity type. For this reason,light incident into the photodiode array is reflected, scattered, ordiffused by the surface with the irregular asperity formed therein, totravel through a long distance in the silicon substrate. This causes thelight incident into the photodiode to be mostly absorbed by thephotodetecting channels, without passing through the photodiode array(silicon substrate). In the photodiode array, therefore, the traveldistance of the light incident into the photodiode array becomes longand the distance of absorption of light also becomes long, thusimproving the spectral sensitivity characteristic in the red tonear-infrared wavelength band.

In the present invention, the irregular asperity is formed in thesurface of the semiconductor layer of the first conductivity type. Thisinduces recombination of unnecessary carriers generated independent oflight on the surface side where the irregular asperity is formed, so asto reduce dark current. The semiconductor layer of the firstconductivity type functions as an accumulation layer and preventscarriers generated by light near the surface of the semiconductor layerof the first conductivity type, from being trapped in the surface. Forthis reason, the carriers generated by light efficiently migrate to themultiplication regions, so as to improve the photodetection sensitivityof the photodiode array.

Another photodiode array according to the present invention is aphotodiode array in which a plurality of photodetecting channels fordetection target light to be entered thereinto are formed on a siliconsubstrate having a semiconductor layer of a first conductivity type, thephotodiode array comprising: an epitaxial semiconductor layer of thefirst conductivity type formed on the semiconductor layer of the firstconductivity type, and having a plurality of multiplication regions foravalanche multiplication of carriers generated with incidence of thedetection target light, so that the multiplication regions correspond tothe respective photodetecting channels; a semiconductor region of asecond conductivity type formed in the epitaxial semiconductor layer ofthe first conductivity type and forming pn junctions at an interface tothe epitaxial semiconductor layer; and a plurality of resistors eachhaving two end portions, provided for the respective photodetectingchannels, and each electrically connected through one of the endportions to the semiconductor region of the second conductivity type inthe epitaxial semiconductor layer and connected through the other of theend portions to a signal conducting wire, wherein an irregular asperityis formed in at least a surface corresponding to the photodetectingchannels in the semiconductor layer of the first conductivity type, andwherein at least the surface corresponding to the photodetectingchannels in the semiconductor layer of the first conductivity type isoptically exposed.

In the photodiode array according to the present invention, the pnjunctions are composed of the epitaxial semiconductor layer of the firstconductivity type and the semiconductor region of the secondconductivity type formed in the semiconductor layer. The multiplicationregions are formed in the epitaxial semiconductor layer where the pnjunctions are substantialized, and the multiplication regionscorresponding to the respective photodetecting channels are present inthe epitaxial semiconductor layer. Therefore, the photodiode array hasno end portions (edges) of the pn junctions to cause edge breakdown whenoperated in a Geiger mode, and thus there is no need for providing aguard ring. For this reason, the photodiode array can have a higheraperture rate.

According to the present invention, as described above, the traveldistance of light incident into the photodiode array becomes long andthe distance of absorption of light also becomes long, thus improvingthe spectral sensitivity characteristic in the red to near-infraredwavelength band. The semiconductor layer of the first conductivity typefunctions as an accumulation layer and in the present invention, it isfeasible to reduce the dark current and improve the photodetectionsensitivity of the photodiode.

Preferably, the irregular asperity is further formed in a surfacecorresponding to a region between the plurality of photodetectingchannels in the semiconductor layer of the first conductivity type andthe surface is optically exposed. In this case, the light incident intothe region between the plurality of photodetecting channels is alsoreflected, scattered, or diffused by the surface with the irregularasperity formed therein, to be absorbed by any one of the photodetectingchannels. Therefore, the detection sensitivity is not lowered betweenthe photodetecting channels, so as to further improve the photodetectionsensitivity.

In the photodiode array according to the present invention, a portion inthe silicon substrate where the plurality of photodetecting channels areformed may be thinned while leaving a surrounding region around thethinned portion. In this case, it is feasible to obtain the photodiodearray of a front-illuminated type and a back-thinned type.

In the photodiode array according to the present invention, preferably,a thickness of the semiconductor layer of the first conductivity type islarger than a height difference of the irregular asperity. In this case,as described above, it is feasible to ensure the operational effect asan accumulation layer by the first conductivity type semiconductorlayer.

A photodiode according to the present invention is one comprising: asilicon substrate comprised of a semiconductor of a first conductivitytype, having a first principal surface and a second principal surfaceopposed to each other, and having a semiconductor region of a secondconductivity type formed on the first principal surface side, wherein onthe silicon substrate, an accumulation layer of the first conductivitytype having a higher impurity concentration than the silicon substrateis formed on the second principal surface side and an irregular asperityis formed in at least a region opposed to the semiconductor region ofthe second conductivity type in the second principal surface, andwherein the region opposed to the semiconductor region of the secondconductivity type in the second principal surface of the siliconsubstrate is optically exposed.

In the photodiode according to the present invention, as describedabove, the travel distance of light incident into the photodiode becomeslong and the distance of absorption of light also becomes long, so as toimprove the spectral sensitivity characteristic in the red tonear-infrared wavelength band. Furthermore, the accumulation layer ofthe first conductivity type formed on the second principal surface sideof the silicon substrate reduces the dark current and improves thephotodetection sensitivity of the photodiode.

Preferably, a portion in the silicon substrate corresponding to thesemiconductor region of the second conductivity type is thinned from thesecond principal surface side while leaving a surrounding region aroundthe thinned portion. In this case, the photodiode can be obtained withrespective light incident surfaces on the first principal surface andsecond principal surface sides of the silicon substrate.

Preferably, a thickness of the accumulation layer of the firstconductivity type is larger than a height difference of the irregularasperity. In this case, as described above, it is feasible to ensure theoperational effect by the accumulation layer.

Advantageous Effects of Invention

The present invention provides the silicon photodiode and siliconphotodiode array as the photodiode and the photodiode array with thesufficient spectral sensitivity characteristic in the near-infraredwavelength band.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing for explaining a manufacturing method of aphotodiode according to the first embodiment.

FIG. 2 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 3 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 4 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 5 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 6 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 7 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 8 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 9 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 10 is a drawing for explaining the manufacturing method of thephotodiode according to the first embodiment.

FIG. 11 is a drawing showing a configuration of the photodiode accordingto the first embodiment.

FIG. 12 is a diagram showing changes of spectral sensitivity versuswavelength in Example 1 and Comparative Example 1.

FIG. 13 is a diagram showing changes of temperature coefficient versuswavelength in Example 1 and Comparative Example 1.

FIG. 14 is a drawing for explaining a manufacturing method of aphotodiode according to the second embodiment.

FIG. 15 is a drawing for explaining the manufacturing method of thephotodiode according to the second embodiment.

FIG. 16 is a drawing for explaining the manufacturing method of thephotodiode according to the second embodiment.

FIG. 17 is a drawing for explaining a manufacturing method of aphotodiode according to the third embodiment.

FIG. 18 is a drawing for explaining the manufacturing method of thephotodiode according to the third embodiment.

FIG. 19 is a drawing for explaining the manufacturing method of thephotodiode according to the third embodiment.

FIG. 20 is a drawing for explaining the manufacturing method of thephotodiode according to the third embodiment.

FIG. 21 is a drawing for explaining the manufacturing method of thephotodiode according to the third embodiment.

FIG. 22 is a drawing for explaining a manufacturing method of aphotodiode according to the fourth embodiment.

FIG. 23 is a drawing for explaining the manufacturing method of thephotodiode according to the fourth embodiment.

FIG. 24 is a drawing for explaining the manufacturing method of thephotodiode according to the fourth embodiment.

FIG. 25 is a plan view schematically showing a photodiode arrayaccording to the fifth embodiment.

FIG. 26 is a drawing schematically showing a cross-sectionalconfiguration along the line XXVI-XXVI in FIG. 25.

FIG. 27 is a drawing schematically explaining a connection relation ofeach photodetecting channel with a signal conducting wire and aresistor.

FIG. 28 is a drawing schematically showing a cross-sectionalconfiguration of a first modification example of the photodiode array ofthe fifth embodiment.

FIG. 29 is a drawing schematically showing a cross-sectionalconfiguration of a second modification example of the photodiode arrayof the fifth embodiment.

FIG. 30 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to the sixth embodiment.

FIG. 31 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to the seventh embodiment.

FIG. 32 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to the eighth embodiment.

FIG. 33 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 26.

FIG. 34 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 28.

FIG. 35 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 29.

FIG. 36 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 30.

FIG. 37 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 31.

FIG. 38 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 32.

FIG. 39 is a drawing schematically showing an example of a mountedstructure of a photodiode array.

FIG. 40 is a drawing schematically showing an example of a mountedstructure of a photodiode array.

DESCRIPTION OF EMBODIMENTS

The preferred embodiments of the present invention will be describedbelow in detail with reference to the accompanying drawings. In thedescription, the same elements or elements with the same functionalitywill be denoted by the same reference signs, without redundantdescription.

First Embodiment

A method for manufacturing a photodiode according to the firstembodiment will be described with reference to FIGS. 1 to 10. FIGS. 1 to10 are drawings for explaining the manufacturing method of thephotodiode according to the first embodiment.

The first step is to prepare an n⁻ type semiconductor substrate 1comprised of silicon (Si) crystal and having a first principal surface 1a and a second principal surface 1 b opposed to each other (cf. FIG. 1).The n⁻ type semiconductor substrate 1 has the thickness of about 300 μmand the resistivity of about 1 kΩ·cm. In the present embodiment, a “highimpurity concentration” refers to, for example, an impurityconcentration of not less than about 1×10¹⁷ cm⁻³ and is denoted by sign“+” attached to conductivity type. A “low impurity concentration” refersto, for example, an impurity concentration of not more than about 1×10¹⁵cm⁻³ and is denoted by sign “−” attached to conductivity type. Examplesof n-type impurities include antimony (Sb), arsenic (As), and so on, andexamples of p-type impurities include boron (B) and others.

Next, a p⁺ type semiconductor region 3 and an n⁺ type semiconductorregion 5 are formed on the first principal surface 1 a side of the n⁻type semiconductor substrate 1 (cf. FIG. 2). The p⁺ type semiconductorregion 3 is formed by diffusing a p-type impurity in a highconcentration from the first principal surface 1 a side in the n⁻ typesemiconductor substrate 1, using a mask opening in a central region. Then⁺ type semiconductor region 5 is formed by diffusing an n-type impurityin a higher concentration than in the n⁻ type semiconductor substrate 1,from the first principal surface 1 a side in the n⁻ type semiconductorsubstrate 1 so as to surround the p⁺ type semiconductor region 3, usinganother mask opening in a peripheral region. The p⁺ type semiconductorregion 3 has the thickness of, for example, about 0.55 μm and the sheetresistance of, for example, 44 Ω/sq. The n⁺ type semiconductor region 5has the thickness of, for example, about 1.5 μm and the sheet resistanceof, for example, 12 Ω/sq.

Next, an insulating layer 7 is formed on the first principal surface 1 aside of the n⁻ type semiconductor substrate 1 (cf. FIG. 3). Theinsulating layer 7 is comprised of SiO₂ and is formed by thermaloxidation of the n⁻ type semiconductor substrate 1. The insulating layer7 has the thickness of, for example, about 0.1 μm. Thereafter, a contacthole H1 is formed in the insulating layer 7 on the p⁺ type semiconductorregion 3 and a contact hole H2 is formed in the insulating layer 7 onthe n⁺ type semiconductor region 5. An antireflective (AR) layercomprised of SiN may be formed instead of the insulating layer 7.

Next, a passivation layer 9 is formed on the second principal surface 1b of the n⁻ type semiconductor substrate 1 and on the insulating layer 7(cf. FIG. 4). The passivation layer 9 is comprised of SiN and is formed,for example, by the plasma CVD process. The passivation layer 9 has thethickness of, for example, 0.1 μm. Then the n⁻ type semiconductorsubstrate 1 is polished from the second principal surface 1 b sidebefore the thickness of the n⁻ type semiconductor substrate 1 reaches adesired thickness (cf. FIG. 5). This process removes the passivationlayer 9 from on the second principal surface 1 b of the n⁻ typesemiconductor substrate 1, thereby exposing the n⁻ type semiconductorsubstrate 1. A surface exposed by polishing is also referred to hereinas the second principal surface 1 b. The desired thickness is, forexample, 270 μm.

Next, the second principal surface 1 b of the n⁻ type semiconductorsubstrate 1 is subjected to irradiation with a pulsed laser beam PL,thereby forming an irregular asperity 10 (cf. FIG. 6). In this step, asshown in FIG. 7, the n⁻ type semiconductor substrate 1 is placed in achamber C, and the n⁻ type semiconductor substrate 1 is irradiated withthe pulsed laser beam PL from a pulse laser generating device PLDlocated outside the chamber C. The chamber C has a gas inlet port G_(IN)and a gas outlet port G_(OUT). An inert gas (e.g., nitrogen gas, argongas, or the like) is introduced through the gas inlet port G_(IN) anddischarged through the gas outlet port G_(OUT), thereby forming an inertgas flow G_(f) in the chamber C. Dust and other materials made duringthe irradiation with the pulsed laser beam PL are discharged as trappedinto the inert gas flow G_(f), to the outside of the chamber C, therebypreventing processing debris, dust, and other materials from attachingto the n⁻ type semiconductor substrate 1.

In the present embodiment, the pulse laser generating device PLD to beused is a picosecond to femtosecond pulse laser generating device and apicosecond to femtosecond pulsed laser beam is applied across the entirearea of the second principal surface 1 b. The second principal surface 1b is roughened by the picosecond to femtosecond pulsed laser beam,whereby the irregular asperity 10 is formed throughout the entire areaof the second principal surface 1 b, as shown in FIG. 8. The irregularasperity 10 has facets intersecting with a direction perpendicular tothe first principal surface 1 a. The height difference of asperity 10is, for example, about 0.5 to 10 μm and the spacing of projections inthe asperity 10 is about 0.5 to 10 μm. The picosecond to femtosecondpulsed laser beam has the pulse duration of, for example, about 50 fs-2ps, the intensity of, for example, about 4 to 16 GW, and the pulseenergy of, for example, about 200 to 800 μJ/pulse. More generally, thepeak intensity is 3×10¹¹ to 2.5×10¹³ (W/cm²) and the fluence is about0.1 to 1.3 (J/cm²). FIG. 8 is an SEM image resulting from observation ofthe irregular asperity 10 formed in the second principal surface 1 b.

Next, an accumulation layer 11 is formed on the second principal surface1 b side of the n⁻ type semiconductor substrate 1 (cf. FIG. 9). In thisstep, the accumulation layer 11 is formed by ion implantation ordiffusion of an n-type impurity from the second principal surface 1 bside in the n⁻ type semiconductor substrate 1 so that an impurityconcentration thereof becomes higher than that of the n⁻ typesemiconductor substrate 1. The accumulation layer 11 has the thicknessof, for example, about 1 μm.

Next, the n⁻ type semiconductor substrate 1 is subjected to a thermaltreatment (annealing). In this step, the n⁻ type semiconductor substrate1 is heated, for example, in the temperature range of about 800 to 1000°C. under an ambience of N₂ gas for about 0.5 to 1 hour.

Next, the passivation layer 9 formed on the insulating layer 7 isremoved and thereafter electrodes 13, 15 are formed (cf. FIG. 10). Theelectrode 13 is formed in the contact hole H1 and the electrode 15 inthe contact hole H2. The electrodes 13, 15 each are comprised ofaluminum (Al) or the like and have the thickness of, for example, about1 μm. This completes the photodiode PD1.

The photodiode PD1 is provided with the n⁻ type semiconductor substrate1, as shown in FIG. 10. The p⁺ type semiconductor region 3 and the n⁺type semiconductor region 5 are formed on the first principal surface 1a side of the n⁻ type semiconductor substrate 1 and a pn junction isformed between the n⁻ type semiconductor substrate 1 and the p⁺ typesemiconductor region 3. The electrode 13 is in electrical contact withand connection to the p⁺ type semiconductor region 3 through the contacthole H1. The electrode 15 is in electrical contact with and connectionto the n⁺ type semiconductor region 5 through the contact hole H2.

The irregular asperity 10 is formed in the second principal surface 1 bof the n⁻ type semiconductor substrate 1. The accumulation layer 11 isformed on the second principal surface 1 b side of the n⁻ typesemiconductor substrate 1 and the second principal surface 1 b isoptically exposed. That the second principal surface 1 b is opticallyexposed encompasses not only the case where the second principal surface1 b is in contact with ambient gas such as air, but also the case wherean optically transparent film is formed on the second principal surface1 b.

In the photodiode PD1, the irregular asperity 10 is formed in the secondprincipal surface 1 b. For this reason, light L incident into thephotodiode PD1 is reflected, scattered, or diffused by the asperity 10,as shown in FIG. 11, to travel through a long distance in the n⁻ typesemiconductor substrate 1.

Normally, Si has the refractive index n=3.5 and air the refractive indexn=1.0. In a photodiode, when light is incident from a direction normalto a light incident surface, light remaining unabsorbed in thephotodiode (silicon substrate) is separated into a light componentreflected on the back surface to the light incident surface and a lightcomponent passing through the photodiode. The light passing through thephotodiode does not contribute to the sensitivity of the photodiode. Thelight component reflected on the back surface to the light incidentsurface, if absorbed in the photodiode, becomes a photocurrent. A lightcomponent still remaining unabsorbed is reflected or transmitted by thelight incident surface as the light component having reached the backsurface to the light incident surface was.

In the photodiode PD1, where light L is incident from the directionnormal to the light incident surface (first principal surface 1 a), whenthe light reaches the irregular asperity 10 formed in the secondprincipal surface 1 b, light components arriving thereat at angles ofnot less than 16.6° to a direction of emergence from the asperity 10 aretotally reflected by the asperity 10. Since the asperity 10 is formedirregularly, it has various angles to the emergence direction and thetotally reflected light components diffuse into various directions. Forthis reason, the totally reflected light components include lightcomponents absorbed inside the n⁻ type semiconductor substrate 1 andlight components arriving at the first principal surface 1 a and sidefaces.

Since the light components arriving at the first principal surface 1 aand side faces travel in various directions because of the diffusion onthe asperity 10, the light components arriving at the first principalsurface 1 a and the side faces are extremely highly likely to be totallyreflected on the first principal surface 1 a and the side faces. Thelight components totally reflected on the first principal surface 1 aand the side faces are repeatedly totally reflected on different facesto further increase their travel distance. The light L incident into thephotodiode PD1 is absorbed in the n⁻ type semiconductor substrate 1during travel through the long distance inside the n⁻ type semiconductorsubstrate 1 to be detected as a photocurrent.

The light L incident into the photodiode PD1 mostly travels, withoutbeing transmitted by the photodiode PD1, through the long traveldistance to be absorbed in the n⁻ type semiconductor substrate 1.Therefore, the photodiode PD1 is improved in the spectral sensitivitycharacteristic in the red to near-infrared wavelength band.

If a regular asperity is formed in the second principal surface 1 b, thelight components arriving at the first principal surface 1 a and theside faces are diffused by the asperity but travel in uniformdirections. Therefore, the light components arriving at the firstprincipal surface 1 a and the side faces are less likely to be totallyreflected on the first principal surface 1 a and the side faces. Thisresults in increase in light passing through the first principal surface1 a and the side faces, and through the second principal surface 1 b,and thus the travel distance of the light incident into the photodiodemust be short. As a result, it becomes difficult to improve the spectralsensitivity characteristic in the near-infrared wavelength band.

An experiment was conducted in order to check the effect of improvementin the spectral sensitivity characteristic in the near-infraredwavelength band by the first embodiment.

We fabricated a photodiode with the above-described configuration(referred to as Example 1) and a photodiode without the irregularasperity in the second principal surface of the n⁻ type semiconductorsubstrate (referred to as Comparative Example 1), and investigated theirspectral sensitivity characteristics. Example 1 and Comparative Example1 have the same configuration, except for the formation of the irregularasperity by irradiation with the pulsed laser beam. The size of the n⁻type semiconductor substrate 1 was set to 6.5 mm×6.5 mm. The size of thep⁺ type semiconductor region 3, or a photosensitive region was set to5.8 mm×5.8 mm. A bias voltage VR applied to the photodiodes was set to 0V.

The results are shown in FIG. 12. In FIG. 12, the spectral sensitivitycharacteristic of Example 1 is represented by T1 and the spectralsensitivity characteristic of Comparative Example 1 by characteristicT2. In FIG. 12, the vertical axis represents the spectral sensitivity(mA/W) and the horizontal axis the wavelength of light (nm). Acharacteristic indicated by a chain line represents a spectralsensitivity characteristic where the quantum efficiency (QE) is 100%,and a characteristic indicated by a dashed line, a spectral sensitivitycharacteristic where the quantum efficiency is 50%.

As seen from FIG. 12, for example at 1064 nm, the spectral sensitivityin Comparative Example 1 is 0.2 A/W (QE=25%,) whereas the spectralsensitivity in Example 1 is 0.6 A/W (QE=72%,); thus the spectralsensitivity in the near-infrared wavelength band is drasticallyimproved.

We also checked temperature characteristics of spectral sensitivity inExample 1 and Comparative Example 1. We investigated the spectralsensitivity characteristics with increase in ambient temperature from25° C. to 60° C. and calculated a rate (temperature coefficient) ofspectral sensitivity at 60° C. to spectral sensitivity at 25° C. Theresults are shown in FIG. 13. In FIG. 13, the characteristic oftemperature coefficient of Example 1 is represented by T3 and that ofComparative Example 1 by characteristic T4. In FIG. 13, the verticalaxis represents the temperature coefficient (%/° C.) and the horizontalaxis the wavelength of light (nm).

As seen from FIG. 13, for example at 1064 nm, the temperaturecoefficient in Comparative Example 1 is 0.7%/° C., whereas thetemperature coefficient in Example 1 is 0.2%/° C., demonstrating lowertemperature dependence. In general, an increase in temperature leads toan increase in spectral sensitivity because of increase in absorptioncoefficient and decrease in bandgap energy. In Example 1, since thespectral sensitivity is sufficiently high even at room temperature, thechange of spectral sensitivity due to temperature rise is smaller thanin Comparative Example 1.

In the photodiode PD1, the accumulation layer 11 is formed on the secondprincipal surface 1 b side of the n⁻ type semiconductor substrate 1.This induces recombination of unnecessary carriers generated independentof light on the second principal surface 1 b side, which can reduce darkcurrent. The accumulation layer 11 prevents carriers generated by lightnear the second principal surface 1 b, from being trapped in the secondprincipal surface 1 b. For this reason, the carriers generated by lightefficiently migrate to the pn junction portion, which can furtherimprove the photodetection sensitivity of the photodiode PD1.

In the first embodiment, after the formation of the accumulation layer11, the n⁻ type semiconductor substrate 1 is subjected to the thermaltreatment. This treatment restores the crystallinity of the n⁻ typesemiconductor substrate 1, which can prevent such a problem as increaseof dark current.

In the first embodiment, after the thermal treatment of the n⁻ typesemiconductor substrate 1, the electrodes 13, 15 are formed. Thisprevents the electrodes 13, 15 from melting during the thermaltreatment, even in the case where the electrodes 13, 15 are made of ametal with a relatively low melting point. Therefore, the electrodes 13,15 can be appropriately formed without being affected by the thermaltreatment.

In the first embodiment, the irregular asperity 10 is formed by theirradiation with the picosecond to femtosecond pulsed laser beam. Thispermits the irregular asperity 10 to be appropriately and readilyformed.

Second Embodiment

A method for manufacturing a photodiode according to the secondembodiment will be described with reference to FIGS. 14 to 16. FIGS. 14to 16 are drawings for explaining the manufacturing method of thephotodiode according to the second embodiment.

The manufacturing method of the second embodiment, up to the polishingof the n⁻ type semiconductor substrate 1 from the second principalsurface 1 b side, is the same as the manufacturing method of the firstembodiment, and the description of the previous steps before it isomitted herein. After the n⁻ type semiconductor substrate 1 is polishedfrom the second principal surface 1 b side to obtain the n⁻ typesemiconductor substrate 1 in the desired thickness, the accumulationlayer 11 is formed on the second principal surface 1 b side of the n⁻type semiconductor substrate 1 (cf. FIG. 14). The formation of theaccumulation layer 11 is carried out in the same manner as in the firstembodiment. The accumulation layer 11 has the thickness of, for example,about 1 μm.

Next, the second principal surface 1 b of the n⁻ type semiconductorsubstrate 1 is irradiated with the pulsed laser beam PL to form theirregular asperity 10 (cf. FIG. 15). The formation of the irregularasperity 10 is carried out in the same manner as in the firstembodiment.

Next, as in the first embodiment, the n⁻ type semiconductor substrate 1is subjected to a thermal treatment. Thereafter, the passivation layer 9formed on the insulating layer 7 is removed and then the electrodes 13,15 are formed (cf. FIG. 16). This completes the photodiode PD2.

In the second embodiment, as in the first embodiment, the traveldistance of light incident into the photodiode PD2 also becomes long andthe distance of absorption of light also becomes long. This allows thephotodiode PD2 also to be improved in the spectral sensitivitycharacteristic in the red to near-infrared wavelength band.

In the second embodiment, the thickness of the accumulation layer 11 islarger than the height difference of the irregular asperity 10. For thisreason, even if the irregular asperity 10 is formed by the irradiationwith the pulsed laser beam after the formation of the accumulation layer11, the accumulation layer 11 remains with certainty. Therefore, it isfeasible to ensure the operational effect by the accumulation layer 11.

Third Embodiment

A method for manufacturing a photodiode according to the thirdembodiment will be described with reference to FIGS. 17 to 21. FIGS. 17to 21 are drawings for explaining the manufacturing method of thephotodiode according to the third embodiment.

The manufacturing method of the third embodiment, up to the formation ofthe passivation layer 9, is the same as the manufacturing method of thefirst embodiment, and the description of the previous steps before it isomitted herein. After the formation of the passivation layer 9, aportion corresponding to the p⁺ type semiconductor region 3 in the n⁻type semiconductor substrate 1 is thinned from the second principalsurface 1 b side while leaving a surrounding region around the thinnedportion (cf. FIG. 17). The thinning of the n⁻ type semiconductorsubstrate 1 is carried out, for example, by anisotropic etching based onalkali etching using a potassium hydroxide solution, TMAH(tetramethylammonium hydroxide solution), or the like. The thinnedportion of the n⁻ type semiconductor substrate 1 has the thickness of,for example, about 100 μm, and the surrounding region around it has thethickness of, for example, about 300 μm.

Next, the n⁻ type semiconductor substrate 1 is polished from the secondprincipal surface 1 b side before the thickness of the surroundingregion of the n⁻ type semiconductor substrate 1 reaches a desiredthickness (cf. FIG. 18). The desired thickness herein is, for example,270 μm.

Next, the second principal surface 1 b of the n⁻ type semiconductorsubstrate 1 is irradiated with the pulsed laser beam PL to form theirregular asperity 10 (cf. FIG. 19). The formation of the irregularasperity 10 is carried out in the same manner as in the firstembodiment.

Next, the accumulation layer 11 is formed on the second principalsurface 1 b side of the thinned portion of the n⁻ type semiconductorsubstrate 1 (cf. FIG. 20). The formation of the accumulation layer 11 iscarried out in the same manner as in the first embodiment. Theaccumulation layer 11 has the thickness of, for example, about 3 μm.

Next, as in the first embodiment, the n⁻ type semiconductor substrate 1is subjected to a thermal treatment and thereafter, the passivationlayer 9 framed on the insulating layer 7 is removed, followed byformation of the electrodes 13, 15 (cf. FIG. 21). This completes thephotodiode PD3.

In the third embodiment, as in the first and second embodiments, thetravel distance of light incident into the photodiode PD3 also becomeslong and the distance of absorption of light also becomes long. Thisallows the photodiode PD3 also to be improved in the spectralsensitivity characteristic in the red to near-infrared wavelength band.

In the third embodiment, prior to the formation of the irregularasperity 10, the portion corresponding to the p⁺ type semiconductorregion 3 in the n⁻ type semiconductor substrate 1 is thinned from thesecond principal surface 1 b side while leaving the surrounding regionaround the thinned portion. This permits the photodiode PD3 to be formedwith respective light incident surfaces on the first principal surface 1a and the second principal surface 1 b sides of the n⁻ typesemiconductor substrate 1.

Fourth Embodiment

A method for manufacturing a photodiode according to the fourthembodiment will be described with reference to FIGS. 22 to 24. FIGS. 22to 24 are drawings for explaining the manufacturing method of thephotodiode according to the fourth embodiment.

The manufacturing method of the fourth embodiment, up to the thinning ofthe n⁻ type semiconductor substrate 1, is the same as the manufacturingmethod of the third embodiment, and the description of the previoussteps before it is omitted herein. After the n⁻ type semiconductorsubstrate 1 is polished from the second principal surface 1 b side toobtain the n⁻ type semiconductor substrate 1 in the desired thickness,the accumulation layer 11 is formed on the second principal surface 1 bside of the thinned portion of the n⁻ type semiconductor substrate 1(cf. FIG. 22). The formation of the accumulation layer 11 is carried outin the same manner as in the first embodiment. The accumulation layer 11has the thickness of, for example, about 3 μm.

Next, the second principal surface 1 b of the n⁻ type semiconductorsubstrate 1 is irradiated with the pulsed laser beam PL to form theirregular asperity 10 (cf. FIG. 23). The formation of the irregularasperity 10 is carried out in the same manner as in the firstembodiment.

Next, the n⁻ type semiconductor substrate 1 is subjected to a thermaltreatment as in the first embodiment. Then the passivation layer 9formed on the insulating layer 7 is removed and thereafter, theelectrodes 13, 15 are formed (cf. FIG. 24). This completes thephotodiode PD4.

In the fourth embodiment, as in the first to third embodiments, thetravel distance of light incident into the photodiode PD4 also becomeslong and the distance of absorption of light also becomes long. Thisallows the photodiode PD4 also to be improved in the spectralsensitivity characteristic in the red to near-infrared wavelength band.

In the fourth embodiment, prior to the formation of the accumulationlayer 11, the portion corresponding to the p⁺ type semiconductor region3 in the n⁻ type semiconductor substrate 1 is thinned from the secondprincipal surface 1 b side while leaving the surrounding region aroundthe thinned portion. This permits the photodiode PD4 to be formed withrespective light incident surfaces on the first principal surface 1 aand the second principal surface 1 b sides of the n⁻ type semiconductorsubstrate 1.

Fifth Embodiment

A configuration of a photodiode array PDA1 according to the fifthembodiment will be described with reference to FIGS. 25 and 26. FIG. 25is a plan view schematically showing the photodiode array PDA1 of thefifth embodiment. FIG. 26 is a drawing showing a cross-sectionalconfiguration along the line XXVI-XXVI of the photodiode array PDA1shown in FIG. 25.

The photodiode array PDA1 is composed of a plurality of semiconductorlayers and an insulating layer layered on a substrate 22. As shown inFIG. 25, the photodiode array PDA1 is a multichannel avalanchephotodiode for photon counting in which a plurality of photodetectingchannels CH for detection target light to be entered thereinto arefanned in a matrix pattern (4×4 in the present embodiment). There aresignal conducting wires 23, resistors 24, and an electrode pad 25provided on the top side of the photodiode array PDA1. The substrate 22has, for example, a square shape about 1 mm on each side. Eachphotodetecting channel CH has, for example, a square shape.

The signal conductor wire 23 consists of a readout portion 23 a,connecting portions 23 b, and channel peripheral portions 23 c. Thereadout portion 23 a transfers a signal output from each photodetectingchannel CH. The connecting portion 23 b connects each resistor 24 andthe readout portion 23 a. Each channel peripheral portion 23 c is routedso as to surround the periphery of the photodetecting channel CH. Thereadout portion 23 a is connected to each of the photodetecting channelsCH arranged in two adjacent columns with the readout portion 23 a inbetween, and is connected at one end thereof to the electrode pad 25.Since in the present embodiment the photodiodes are arranged in the 4×4matrix pattern, there are two readout portions 23 a as wiring on thephotodiode array PDA1 and these are connected both to the electrode pad25. The signal conducting wires 23 are comprised, for example, ofaluminum (Al).

The resistor 24 is provided for each photodetecting channel CH throughone end portion 24 a and the channel peripheral portion 23 c and isconnected through the other end portion 24 b and the connecting portion23 b to the readout portion 23 a. A plurality of resistors 24 (eight inthe present embodiment) connected to an identical readout portion 23 aare connected to the readout portion 23 a. The resistors 24 arecomprised, for example, of polysilicon (Poly-Si).

Next, the cross-sectional configuration of the photodiode array PDA1will be described with reference to FIG. 26. As shown in FIG. 26, thephotodiode array PDA1 is provided with a substrate 22 having asemiconductor layer with the conductivity type of n-type (firstconductivity type), a p⁻ type semiconductor layer 33 with theconductivity type of p-type (second conductivity type) formed on thesubstrate 22, p⁺ type semiconductor regions 34 with the conductivitytype of p-type formed on the p⁻ type semiconductor layer 33, aprotecting film 36, a separating portion 40 with the conductivity typeof n-type (first conductivity type) formed in the p⁻ type semiconductorlayer 33, and the aforementioned signal conducting wires 23 andresistors 24 formed on the protecting film 36. The detection targetlight is incident from the top side or the bottom side in FIG. 26.

The substrate 22 has a substrate member S, an insulating film 31 formedon the substrate member S, and an n⁺ type semiconductor layer 32 formedon the insulating film 31. The substrate member S is comprised of Si(silicon). The insulating film 31 is comprised, for example, of SiO₂(silicon oxide). The n⁺ type semiconductor layer 32 is a semiconductorlayer with the conductivity type of n-type comprised of Si and having ahigh impurity concentration. The thickness of the n⁺ type semiconductorlayer 32 is, for example, 1 μm-12 μm.

The p⁻ type semiconductor layer 33 is an epitaxial semiconductor layerwith the conductivity type of p-type having a low impurityconcentration. The p⁻ type semiconductor layer 33 forms pn junctions atthe interface to the substrate 22. The p⁻ type semiconductor layer 33has a plurality of multiplication regions AM for avalanchemultiplication of carriers generated with incidence of the detectiontarget light, corresponding to the respective photodetecting channelsCH. The thickness of the p⁻ type semiconductor layer 33 is, for example,3 μm-5 μm. The p⁻ type semiconductor layer 33 is comprised of Si.Therefore, the n⁺ type semiconductor layer 32 and the p⁻ typesemiconductor layer 33 constitute a silicon substrate.

The p⁺ type semiconductor regions 34 are formed on the p⁻ typesemiconductor layer 33, corresponding to the multiplication regions AMof the respective photodetecting channels CH. Namely, eachmultiplication region AM is a region near the interface to the substrate22 in the p⁻ type semiconductor layer 33 located below the p⁺ typesemiconductor region 34 in the lamination direction of semiconductorlayers (which will be referred to hereinafter simply as the laminationdirection). The p⁺ type semiconductor regions 34 are comprised of Si.

The separating portion 40 is formed between the plurality ofphotodetecting channels CH to separate the photodetecting channels CH.Namely, the separating portion 40 is formed so as to form themultiplication regions AM in the p⁻ type semiconductor layer 33 inone-to-one correspondence to the respective photodetecting channels CH.The separating portion 40 is formed in a two-dimensional lattice patternon the substrate 22 so as to completely surround the periphery of eachmultiplication region AM. The separating portion 40 is formed so as topenetrate from the top side to the bottom side of the p⁻ typesemiconductor layer 33 in the lamination direction. The separatingportion 40 is a semiconductor layer with the conductivity type of n-typean impurity of which is comprised, for example, of P and an impurityconcentration of which is high. If the separating portion 40 is formedby diffusion, a long thermal treatment time will be needed. For thisreason, it is considered that the impurity of the n⁺ type semiconductorlayer 32 diffuses into the epitaxial semiconductor layer so as to causea rise of interfaces of the pn junctions. In order to prevent this rise,the separating portion 40 may be formed in such a manner that a trenchis formed by etching near centers of regions corresponding to theseparating portion 40 and thereafter performing diffusion of theimpurity. The details will be described in another embodiment, but alight shielding portion may be formed in the trench groove by fillingthe trench groove with a material to absorb or reflect the light in thewavelength band to be absorbed by the photodetecting channels. In thiscase, it is feasible to prevent crosstalk caused by influence ofemission by avalanche multiplication on neighboring photodetectingchannels.

The p⁻ type semiconductor layer 33, p⁺ type semiconductor regions 34,and separating portion 40 form a flat surface on the top side of thephotodiode array PDA1 and the protecting film 36 is formed thereon. Theprotecting film 36 is made of an insulating layer comprised, forexample, of SiO₂.

The signal conducting wires 23 and resistors 24 are formed on theprotecting film 36. The readout portions 23 a of the signal conductingwires 23 and the resistors 24 are formed above the separating portion40.

The signal conducting wires 23 function as anodes and the photodiodearray may be provided with a transparent electrode layer (e.g., a layercomprised of ITO (Indium Tin Oxide)) over the entire surface on thebottom side (the side without the insulating film 31) of the substrate22, as a cathode though not shown. Alternatively, as a cathode, anelectrode portion may be formed so as to be drawn out to the front side.

Now, a connection relation of each photodetecting channel CH to thesignal conducting wire 23 and resistor 24 will be described withreference to FIG. 27. FIG. 27 is a drawing for schematically explainingthe connection relation of each photodetecting channel CH to the signalconducting wire 23 and resistor 24. As shown in FIG. 27, the p⁺ typesemiconductor region 34 of each photodetecting channel CH is directlyconnected to the signal conducting wire 23 (channel peripheral portion23 c). This establishes electrical connection between the signalconducting wire 23 (channel peripheral portion 23 c) and the p⁻ typesemiconductor layer 33. The p⁻ type semiconductor layer 33 and one end24 a of the resistor 24 are connected through the signal conducting wire23 (channel peripheral portion 23 c) and the other end 24 b of eachresistor 24 is connected through the connecting portion 23 b to thereadout portion 23 a.

In the substrate 22, the region where the plurality of photodetectingchannels CH are formed is thinned from the substrate member S side, soas to remove a portion corresponding to the region where the pluralityof photodetecting channels CH are formed in the substrate member S. Thesubstrate member S exists as a frame portion around the thinned region.By removing the frame portion, the substrate 22 may have a configurationwherein the entire region is thinned, i.e., the whole substrate member Sis removed. The removal of the substrate member S can be implemented byetching (e.g., dry etching or the like), polishing, and so on. In thecase where the substrate member S is removed by dry etching, theinsulating film 31 also functions as an etching stop layer. Theinsulating film 31 exposed after the removal of the substrate member Sis removed as described later.

In the surface of the n⁺ type semiconductor layer 32, the irregularasperity 10 is formed throughout the entire region where the pluralityof photodetecting channels CH are formed. The region where the irregularasperity 10 is formed in the surface of the n⁺ type semiconductor layer32 is optically exposed. That the surface of the n⁺ type semiconductorlayer 32 is optically exposed embraces, not only the case where thesurface of the n⁺ type semiconductor layer 32 is in contact with ambientgas such as air, but also the case where an optically transparent filmis formed on the surface of the n⁺ type semiconductor layer 32. Theirregular asperity 10 may also be formed only in the regions opposed tothe respective photodetecting channels CH.

The irregular asperity 10 is formed by irradiating the insulating film31 exposed after the removal of the substrate member S with a pulsedlaser beam, in the same manner as in the aforementioned embodiments.Namely, when the exposed insulating film 31 is irradiated with thepulsed laser beam, the insulating film 31 is removed and the surface ofthe n⁺ type semiconductor layer 32 is roughened by the pulsed laserbeam, thereby forming the irregular asperity 10. A pulse lasergenerating device to irradiate the pulsed laser beam can be a picosecondto femtosecond pulse laser generating device. The irregular asperity 10has facets intersecting with the direction perpendicular to the surfaceof the n⁺ type semiconductor layer 32. The height difference of theasperity 10 is, for example, about 0.5-10 μm and the spacing ofprojections in the asperity 10 is about 0.5-10 μm. The picosecond tofemtosecond pulsed laser beam has the pulse duration of, for example,about 50 fs-2 ps, the intensity of, for example, about 4-16 GW, and thepulse energy of, for example, about 200-800 μJ/pulse. More generally,the peak intensity is about 3×10¹¹-2.5×10¹³ (W/cm²) and the fluenceabout 0.1-1.3 (J/cm²).

After the formation of the irregular asperity 10 by irradiation with thepulsed laser beam, the substrate 22 is preferably subjected to a thermaltreatment (anneal). For example, the substrate 22 is heated in thetemperature range of about 800 to 1000° C. in an ambience of N₂ gas orthe like for about 0.5 to 1.0 hour. The foregoing thermal treatmentrestores the crystallinity of the n⁺ type semiconductor layer 32 andthus prevents the problem such as increase of dark current.

When the photodiode array PDA1 configured as described above is used forphoton counting, it is operated under an operation condition called aGeiger mode. In this Geiger mode operation, a reverse voltage (e.g., 50V or more) higher than the breakdown voltage is applied to eachphotodetecting channel CH. When the detection target light is incidentfrom the top side into each photodetecting channel CH in this state, thetarget light is absorbed in each photodetecting channel CH to generate acarrier. The generated carrier migrates as accelerated according to anelectric field in each photodetecting channel CH to be multiplied ineach multiplication region AM. Then the multiplied carriers are takenout through the resistor 24 and through the signal conducting wire 23 tothe outside to be detected based on a wave height value of an outputsignal thereof. Since every channel detecting a photon provides the samequantity of output, the total output from all the channels is detected,thereby counting how many photodetecting channels CH in the photodiodearray PDA1 provided the output. Therefore, the photodiode array PDA1accomplishes the photon counting by the single irradiation operationwith the detection target light.

Incidentally, the irregular asperity 10 is formed in the surface of then⁺ type semiconductor layer 32 in the photodiode array PDA1. For thisreason, the light incident into the photodiode array PDA1 is reflected,scattered, or diffused by the asperity 10 to travel through a longdistance in the photodiode array PDA1.

For example, in the case where the photodiode array PDA1 is used as afront-illuminated type photodiode array and where the light is incidentfrom the protecting film 36 side into the photodiode array PDA1, whenthe light reaches the irregular asperity 10 formed in the surface of then⁺ type semiconductor layer 32, light components arriving thereat atangles of not less than 16.6° to the direction of emergence from theasperity 10 are totally reflected by the asperity 10. Since the asperity10 is formed irregularly, it has various angles relative to theemergence direction and the totally reflected light components diffuseinto various directions. For this reason, the totally reflected lightcomponents include light components absorbed in each photodetectingchannel CH and light components reaching the surface on the protectingfilm 36 side and the side faces of the n⁺ type semiconductor layer 32.

The light components reaching the surface on the protecting film 36 sideand the side faces of the n⁺ type semiconductor layer 32 travel invarious directions because of the diffusion on the asperity 10. For thisreason, the light components reaching the surface on the protecting film36 side and the side faces of the n⁺ type semiconductor layer 32 areextremely highly likely to be totally reflected on the surface on theprotecting film 36 side and the side faces of the n⁺ type semiconductorlayer 32. The light components totally reflected on the surface on theprotecting film 36 side and the side faces of the n⁺ type semiconductorlayer 32 are repeatedly totally reflected on different faces, to furtherincrease their travel distance. While the light incident into thephotodiode array PDA1 travels through the long distance inside thephotodiode array PDA1, it is absorbed in each photodetecting channel CHto be detected as a photocurrent.

In the case where the photodiode array PDA1 is used as a back-thinnedtype photodiode array and where the light is incident from the frontsurface side of the n⁺ type semiconductor layer 32 into the photodiodearray PDA1, the incident light is scattered by the asperity 10 andtravels in various directions in the photodiode array PDA1. The lightcomponents reaching the surface on the protecting film 36 side and theside faces of the n⁺ type semiconductor layer 32 travel in variousdirections because of the diffusion on the asperity 10. For this reason,the light components reaching the surface on the protecting film 36 sideand the side faces of the n⁺ type semiconductor layer 32 are extremelyhighly likely to be totally reflected on each surface. The lightcomponents totally reflected on the surface on the protecting film 36side and the side faces of the n⁺ type semiconductor layer 32 arerepeatedly totally reflected on different faces and reflected,scattered, or diffused on the asperity 10, to further increase theirtravel distance. The light incident into the photodiode array PDA1 isreflected, scattered, or diffused by the asperity 10 to travel throughthe long distance in the photodiode array PDA1, and to be absorbed ineach photodetecting channel CH to be detected as a photocurrent.

The light L incident into the photodiode array PDA1 mostly travelsthrough the long travel distance to be absorbed in each photodetectingchannel CH, without passing through the photodiode array PDA1.Therefore, the photodiode array PDA1 is improved in the spectralsensitivity characteristic in the red to near-infrared wavelength band.

In the fifth embodiment, the irregular asperity 10 is formed in thesurface of the n⁺ type semiconductor layer 32. For this reason, itinduces recombination of unnecessary carriers generated independent oflight on the surface side where the irregular asperity 10 is formed, soas to reduce the dark current. The n⁺ type semiconductor layer 32functions as an accumulation layer to prevent carriers generated bylight near the surface of the n⁺ type semiconductor layer 32 from beingtrapped in the surface. For this reason, the carriers generated by lightefficiently migrate to the multiplication regions AM, so as to improvethe photodetection sensitivity of the photodiode array PDA1.

In the fifth embodiment, the irregular asperity 10 is also formed in thesurface corresponding to the regions between the plurality ofphotodetecting channels CH in the n⁺ type semiconductor layer 32 and thesurface is optically exposed. For this reason, light incident into theregions between the plurality of photodetecting channels CH is alsoreflected, scattered, or diffused by the irregular asperity 10 to beabsorbed in any one of the photodetecting channels CH. Therefore, thedetection sensitivity is not lowered in the regions between thephotodetecting channels CH, whereby the photodetection sensitivity ofthe photodiode array PDA1 is further improved. Incidentally, theplurality of photodetecting channels CH are formed in the fifthembodiment, but each photodetecting channel CH is not one to detect aposition of incidence of light and the output of the array is the sum ofoutputs of the respective photodetecting channels CH. For this reason,crosstalk between the photodetecting channels CH does not matter, andthe point is that incident light is detected by any one of thephotodetecting channels CH.

In the fifth embodiment, the thickness of the n⁺ type semiconductorlayer 32 is larger than the height difference of the irregular asperity10. For this reason, it is feasible to certainly ensure the operationaleffect as an accumulation layer by the n⁺ type semiconductor layer 32.

In the photodiode array PDA1, the pn junctions are composed of the n⁺type semiconductor layer 32 of the substrate 22 and the p⁻ typesemiconductor layer 33 being the epitaxial semiconductor layer formed onthe n⁺ type semiconductor layer 32 of the substrate 22. Themultiplication regions AM are formed in the p⁻ type semiconductor layer33 where the pn junctions are substantialized, and the correspondence ofeach multiplication region AM to each photodetecting channel CH isrealized by the separating portion 40 formed between the photodetectingchannels CH. A pn junction surface is composed of an interface betweenthe n⁺ type semiconductor layer 32 and the p⁻ type semiconductor layer33 and an interface between the separating portion 40 and the p⁻ typesemiconductor layer 33. For this reason, the high-concentration impurityregions are convex and there is no region having a high electric field.Therefore, the photodiode array PDA1 has no ends (edges) of pn junctionswhere edge breakdown occurs in the Geiger mode operation. For thisreason, the photodiode array PDA1 does not have to be provided with aguard ring for the pn junction of each photodetecting channel CH. Thisenables the photodiode array PDA1 to have a drastically high aperturerate.

By achieving the high aperture rate, it also becomes feasible toincrease the detection efficiency of the photodiode array PDA1.

Since the photodetecting channels CH are separated by the separatingportion 40, it becomes feasible to well suppress crosstalk.

Even if in the Geiger mode operation a large voltage difference is madebetween a photodetecting channel with incidence of a photon and achannel without incidence, the channels can be separated well becausethe separating portion 40 is formed between the photodetecting channelsCH.

Since in the photodiode array PDA1 the readout portions 23 a of thesignal conducting wires 23 are formed above the separating portion 40,the signal conducting wires 23 are prevented from crossing above themultiplication regions AM, i.e., above the photodetection surface. Forthis reason, the aperture rate is more increased. Furthermore, it isconsidered to be also effective to suppression of dark current. In thephotodiode array PDA1, the aperture rate is still more increased becausethe resistors 24 are also formed above the separating portion 40.

The inventor of the present application discovered from wavelengthdependence of after pulse that in the case where the n-typesemiconductor substrate was used and the p-type epitaxial semiconductorlayer was formed thereon, some of holes generated in the n-typesemiconductor substrate went late into the multiplication region toproduce an after pulse. In view of this problem, the photodiode arrayPDA1 is constructed by removing the substrate member S from the regionwhere the plurality of photodetecting channels CH are formed, so as tosuppress the after pulse.

A variety of modifications can be applied to the separating portion 40in the fifth embodiment. FIG. 28 is a drawing schematically showing across-sectional configuration of a first modification example of thephotodiode array PDA1 of the fifth embodiment. In the photodiode arrayof the first modification example, a plurality of separating portions 40(two in the present modification example) are formed between thephotodetecting channels CH.

FIG. 29 is a drawing schematically showing a cross-sectionalconfiguration of a second modification example of the photodiode arrayPDA1 of the present embodiment. In the photodiode array of the secondmodification example, the separating portion 40 is formed only in thevicinity of the top surface (detection target light incident surface)without penetrating from the top side to the bottom side of the p⁻ typesemiconductor layer 33 in the lamination direction.

The above embodiment showed the configuration wherein the epitaxialsemiconductor layer had the second conductivity type, but it is alsopossible to adopt a configuration wherein the epitaxial semiconductorlayer has the first conductivity type, second conductivity typesemiconductor regions are provided in the semiconductor layer, and thepn junctions are composed of the first conductivity type epitaxialsemiconductor layer and the second conductivity type semiconductorregions.

The photodiode array PDA1 is mounted on a board WB as shown in FIGS. 39and 40. In FIG. 39, the photodiode array PDA1 is fixed to the board WBby bonding or the like and is electrically connected to wiring formed onthe board WB by wire bonding. In FIG. 40, the photodiode array PDA1 isfixed to a board WB and electrically connected to wiring formed on theboard WB by bumps. In the case where the photodiode array PDA1 isconnected to the board WB by bumps, it is preferable to fill the regionbetween the photodiode array PDA1 and the board WB with an underfillresin. In this case, it is feasible to ensure the connection strengthbetween the photodiode array PDA1 and the board WB.

In FIG. 39, when the photodiode array PDA1 is used as a back-thinnedtype photodiode array, the board WB is preferably optically transparent.Likewise, in FIG. 40, when the photodiode array PDA1 is used as afront-illuminated type photodiode array, the board WB is also preferablyoptically transparent. In this case, the underfill resin to be filled isalso preferably optically transparent.

Sixth Embodiment

A configuration of a photodiode array PDA2 according to the sixthembodiment will be described with reference to FIG. 30. FIG. 30 is adrawing schematically showing a cross-sectional configuration of thephotodiode array PDA2 of the sixth embodiment. The photodiode array PDA2of the sixth embodiment is different from the photodiode array PDA1 ofthe fifth embodiment in that the separating portion 40 has a lightshielding portion.

As shown in FIG. 30, the separating portion 40 includes the lightshielding portion 42 comprised of a material to absorb light in thewavelength band of detection target light (from visible to nearinfrared) to be detected by the photodetecting channels CH. The lightshielding portion 42 is formed so as to be embedded in the separatingportion 40 like a core extending from the top side to the bottom side ofthe p⁻ type semiconductor layer 33. The light shielding portion 42 iscomprised, for example, of a black photoresist obtained by mixing ablack dye or a pigment such as insulated carbon black in a photoresist,or a metal such as tungsten. However, in the case where the materialmaking up the light shielding portion 42 is not an insulating material(e.g., the metal such as tungsten), the light shielding portion 42 needsto be coated with an insulating film such as SiO₂. As also described inthe fifth embodiment, if the separating portion 40 is formed bydiffusion the long thermal treatment time is needed; therefore, it isconsidered that the impurity of the n⁺ type semiconductor layer 32diffuses into the epitaxial semiconductor layer to cause the rise of theinterfaces of the pn junctions. In order to prevent this rise, theseparating portion 40 may be formed by forming a trench near the centersof the regions corresponding to the separating portion 40 by etching andthereafter performing diffusion of the impurity. As shown in FIG. 30,after execution of the impurity diffusion, the n⁺ type semiconductorlayer 32 and the separating portion 40 become continuous. The lightshielding portion may also be formed by filling the remaining trenchgroove with a material to absorb the light in the wavelength band to beabsorbed by the photodetecting channels as described above (or amaterial to reflect the light in the wavelength band to be absorbed bythe photodetecting channels, as described below). This can prevent thecrosstalk caused by influence of emission by avalanche multiplication onneighboring photodetecting channels.

In the sixth embodiment, as in the fifth embodiment, the travel distanceof the light incident into the photodiode array PDA2 becomes long andthe distance of absorption of light also becomes long. This allows thephotodiode array PDA2 also to be improved in the spectral sensitivitycharacteristic in the red to near-infrared wavelength band. Furthermore,the dark current is reduced and the photodetection sensitivity of thephotodiode array PDA2 is also improved.

In the photodiode array PDA2, as in the photodiode array PDA1, there isno ends (edges) of the pn junctions to cause edge breakdown in theGeiger mode operation. For this reason, the photodiode array PDA2 doesnot have to be provided with a guard ring for the pn junction of eachphotodetecting channel CH, either. This allows the photodiode array PDA2to have a higher aperture rate.

When the aperture rate is higher, it also becomes feasible to increasethe detection efficiency of the photodiode array PDA2.

Since the photodetecting channels CH are separated by the separatingportion 40, it is feasible to well suppress the crosstalk.

Since the readout portions 23 a of the signal conducting wires 23 arealso formed above the separating portion 40 in the photodiode arrayPDA2, the aperture rate is more improved. Furthermore, it is consideredto be also effective to suppression of dark current.

Each separating portion 40 includes the light shielding portion 42comprised of the material to absorb the light in the wavelength band ofthe detection target light to be detected by the photodetecting channelsCH. Therefore, the light shielding portion absorbs the detection targetlight, and thus it becomes feasible to well suppress occurrence ofcrosstalk. The light shielding portion 42 is comprised of a materialthat absorbs light in the wavelength band of the detection target lightto be detected by the photodetecting channels CH, particularly, in thevisible to near-infrared wavelength band generated by avalanchemultiplication, in order to prevent the light generated by avalanchemultiplication from affecting the neighboring photodetecting channelsCH. For this reason, it becomes feasible to well suppress occurrence ofcrosstalk.

The light shielding portion 42 does not have to be limited to thematerial that absorbs the light in the visible to near-infrared band,but may be a material that reflects the light in the visible tonear-infrared band. In this case, the light shielding portion reflectsthe detection target light and thus it becomes feasible to well suppressoccurrence of crosstalk. The light shielding portion 42 is comprised ofthe material that reflects light in the wavelength band of the detectiontarget light to be detected by the photodetecting channels CH,particularly, in the visible to near-infrared wavelength band generatedby avalanche multiplication, in order to prevent the light generated byavalanche multiplication from affecting the neighboring photodetectingchannels CH. For this reason, it becomes feasible to well suppressoccurrence of crosstalk.

The light shielding portion 42 does not have to be limited to thematerial absorbing or reflecting the light in the visible tonear-infrared band, but may be any material that absorbs or reflectslight in the wavelength band of the detection target light to bedetected by the photodetecting channels CH. However, the light shieldingportion 42 is preferably comprised of a material that absorbs orreflects light in the wavelength band of the detection target light tobe detected by the photodetecting channels CH, particularly, in thevisible to near-infrared wavelength band generated by avalanchemultiplication, in order to prevent the light generated by avalanchemultiplication from affecting the neighboring photodetecting channelsCH.

The light shielding portion 42 may be comprised of a material with therefractive index lower than that of the separating portion 40. In thiscase, the light is also reflected by the light shielding portion andthus it becomes feasible to well suppress occurrence of crosstalk.

Seventh Embodiment

A configuration of a photodiode array PDA3 according to the seventhembodiment will be described with reference to FIG. 31. FIG. 31 is adrawing for schematically explaining a cross-sectional configuration ofthe photodiode array PDA3 of the seventh embodiment. The photodiodearray PDA3 of the seventh embodiment is different from the photodiodearray PDA1 of the fifth embodiment in that the signal conducting wires23 are formed on a silicon nitride film.

As shown in FIG. 31, the photodiode array PDA3 is provided with asubstrate 22 having a semiconductor layer with the conductivity type ofn-type (first conductivity type), a p-type semiconductor layer 35 withthe conductivity type of p-type (second conductivity type) formed on thesubstrate 22, p⁺ type semiconductor regions 34 with the conductivitytype of p-type formed on the p-type semiconductor layer 35, protectingfilms 36 a, 36 b, a separating portion 40 with the conductivity type ofn-type (first conductivity type) formed in the p-type semiconductorlayer 35, signal conducting wires 23 of aluminum, and resistors 24, forexample, of Ply-Si.

The substrate 22 has an n⁺ type substrate member (not shown), and ann-type semiconductor layer 32 formed on the substrate member.

The p-type semiconductor layer 35 is an epitaxial semiconductor layerwith the conductivity type of p-type having an impurity concentrationlower than that of the p⁺ type semiconductor regions 34. The p-typesemiconductor layer 35 forms pn junctions at its interface to the n-typesemiconductor layer 32 of the substrate 22. The p-type semiconductorlayer 35 has a plurality of multiplication regions AM for avalanchemultiplication of carriers generated with incidence of detection targetlight, corresponding to the respective photodetecting channels CH. Thep-type semiconductor layer 35 is comprised of Si.

The p-type semiconductor layer 35, p⁺ type semiconductor regions 34, andseparating portion 40 form a flat surface on the top side of thephotodiode array PDA3 and the protecting films 36 a, 36 b are formedthereon. The protecting film 36 a is comprised of an insulating film ofsilicon oxide film (SiO₂ film) and the protecting film 36 b is comprisedof an insulating film of silicon nitride (SiN film or Si₃N₄ film).

As shown in FIG. 31, the protecting film 36 a, resistors 24, protectingfilm 36 b, and signal conducting wires 23 are layered in this order onthe separating portion 40. Specifically, the protecting film 36 a islayered on the separating portion 40. The resistors 24 are layered onthe protecting film 36 a. The protecting film 36 b is layered except fora part of each resistor 24 on the protecting film 36 a and on theresistors 24. The signal conducting wires 23 are layered for electricalconnection, on the protecting film 36 b and the parts of resistors 24 onwhich the protecting film 36 b is not layered. Specifically, a readoutportion 23 a of the signal conducting wire 23 is layered betweenresistors 24, and the signal conducting wire 23 as an electricalconnection to the connecting portion 23 b or the channel peripheralportion 23 c is layered for electrical connection on each resistor 24.

As shown in FIG. 31, the protecting film 36 b is layered except for apart on each p⁺ type semiconductor region 34. The channel peripheralportion 23 c of the signal conducting wire 23 for electrical connectionis layered on the part of the p⁺ type semiconductor region 34 withoutdeposition of the protecting film 36 b and on the part of the protectingfilm 36 b layered on the p⁺ type semiconductor region 34.

In the seventh embodiment, as in the fifth and sixth embodiments, thetravel distance of the light incident into the photodiode array PDA3becomes long and the distance of absorption of light also becomes long.This allows the photodiode array PDA3 also to be improved in thespectral sensitivity characteristic in the red to near-infraredwavelength band. Furthermore, the dark current is reduced and thephotodetection sensitivity of the photodiode array PDA3 is improved.

The photodiode array PDA3, like the photodiode array PDA1, has no ends(edges) of the pn junctions to cause edge breakdown in the Geiger modeoperation. For this reason, the photodiode array PDA3 does not have tobe provided with a guard ring for the pn junction of each photodetectingchannel CH, either. This allows the photodiode array PDA3 to have ahigher aperture rate.

When the aperture rate is higher, it is also feasible to increase thedetection efficiency of the photodiode array PDA3.

Since the photodetecting channels CH are separated by the separatingportion 40, it becomes feasible to well suppress crosstalk.

Since the readout portions 23 a of the signal conducting wires 23 arealso formed above the separating portion 40 in the photodiode arrayPDA3, the aperture rate is more improved. Furthermore, it is consideredto be also effective to suppression of dark current.

Since the signal conducting wires 23 are comprised of aluminum, forexample, if they are formed on an oxide film, there will arise a problemthat aluminum leaks into the underlying film with application of highvoltage. In view of this problem, the signal conducting wires 23 areformed on the protecting film 36 b of silicon nitride film in thephotodiode array PDA3. For this reason, aluminum is prevented fromleaking into the underlying film (protecting film 36 b) even withapplication of high voltage to the photodiode array PDA3.

The protecting film 36 b and the protecting film 36 a or the resistor 24are layered under the readout portion 23 a of each signal conductingwire 23. For this reason, aluminum is well prevented from leaking intothe separating portion 40 and the p-type semiconductor layer 35 withapplication of high voltage.

In the photodiode array PDA3, aluminum is suitably prevented fromentering the photodetecting channels CH and separating portion 40 evenwith application of high voltage.

For example, the resistors 24 of polysilicon (Poly-Si) are formed on theprotecting film 36 a, and the protecting film 36 b and signal conductingwires 23 are formed on the resistors 24.

A p-type semiconductor layer may be used instead of the n-typesemiconductor layer 32. In this case, the pn junctions are establishedbetween the p-type semiconductor layer and the n⁺ type substrate memberS (substrate 22) and the multiplication portions AM are formed in thisp-type semiconductor layer.

Eighth Embodiment

A configuration of a photodiode array PDA4 according to the eighthembodiment will be described with reference to FIG. 32. FIG. 32 is adrawing schematically showing a cross-sectional configuration of thephotodiode array PDA4 of the eighth embodiment. The photodiode arrayPDA4 of the eighth embodiment is different from the photodiode arrayPDA1 of the fifth embodiment in that it is not provided with theseparating portion 40.

As shown in FIG. 32, the p⁻ type semiconductor layer 33 has a pluralityof multiplication regions AM so that the multiplication regions AMcorrespond to the respective photodetecting channels CH. The signalconducting wires 23 and resistors 24 are formed between thephotodetecting channels CH.

In the eighth embodiment, as in the fifth to seventh embodiments, thetravel distance of light incident into the photodiode array PDA4 becomeslong and the distance of absorption of light also becomes long. Thisallows the photodiode array PDA4 also to be improved in the spectralsensitivity characteristic in the red to near-infrared wavelength band.Furthermore, the dark current is reduced and the photodetectionsensitivity of the photodiode array PDA4 is improved.

The photodiode array PDA4, like the photodiode array PDA1, has no ends(edges) of the pn junctions to cause edge breakdown in the Geiger modeoperation, either. For this reason, the photodiode array PDA4 does nothave to be provided with a guard ring for the pn junction of eachphotodetecting channel CH, either. This allows the photodiode array PDA4to have a higher aperture rate. Furthermore, since the photodiode arrayPDA4 has no separating portion, it can demonstrate a much higheraperture rate.

When the aperture rate is higher, it is also feasible to increase thedetection efficiency of the photodiode array PDA4.

Since the readout portions 23 a of the signal conducting wires 23 areformed between the photodetecting channels CH in the photodiode arrayPDA4, the aperture rate is more improved. Furthermore, it is consideredto be also effective to suppression of dark current.

The above described the preferred embodiments of the present invention,but it should be noted that the present invention is not always limitedto the above-described embodiments but can be modified in various wayswithout departing from the scope and spirit of the invention.

In the first to fourth embodiments the irregular asperity 10 is formedby irradiating the entire area of the second principal surface 1 b withthe pulsed laser beam, but the present invention is not limited to it.For example, the irregular asperity 10 may also be formed by irradiatingonly the region opposed to the p⁺ type semiconductor region 3 in thesecond principal surface 1 b of the n⁻ type semiconductor substrate 1with the pulsed laser beam.

In the first to fourth embodiments the electrode 15 is in electricalcontact with and connection to the n⁺ type semiconductor region 5 formedon the first principal surface 1 a side of the n⁻ type semiconductorsubstrate 1, but it is not limited only to this example. For example,the electrode 15 may be in electrical contact with and connection to theaccumulation layer 11 formed on the second principal surface 1 b side ofthe n⁻ type semiconductor substrate 1. In this case, the electrode 15 ispreferably formed outside the region opposed to the p⁺ typesemiconductor region 3 in the second principal surface 1 b of the n⁻type semiconductor substrate 1. The reason for it is as follows: if theelectrode 15 is formed in the region opposed to the p⁺ typesemiconductor region 3 in the second principal surface 1 b of the n⁻type semiconductor substrate 1, the irregular asperity 10 formed in thesecond principal surface 1 b is blocked by the electrode 15, causing anevent of reduction in the spectral sensitivity in the near-infraredwavelength band.

The conductivity types of p⁻ type and n⁻ type in the photodiodes PD1-PD4in the first to fourth embodiments may be interchanged so as to bereverse to those described above.

In the fifth to eighth embodiments, the number of photodetectingchannels formed in the photodiode array is not limited to the number(4×4) in the above embodiments. The number of separating portion 40formed between the photodetecting channels CH is not limited to thenumbers shown in the above embodiments and modification examples,either, but it may be, for example, three or more. The signal conductingwires 23 do not have to be formed above the separating portion 40. Theresistors 24 do not have to be formed above the separating portion 40,either. Each of the layers and others does not have to be the oneexemplified in the above embodiments and modification examples. Theconductivity types of p-type and n-type in the above-describedphotodiode arrays PDA1-PDA4 may be interchanged so as to be reverse tothose described above.

FIG. 33 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 26. FIG. 34 is adrawing schematically showing a cross-sectional configuration of aphotodiode array according to a modification example of the layerstructure in the embodiment shown in FIG. 28. FIG. 35 is a drawingschematically showing a cross-sectional configuration of a photodiodearray according to a modification example of the layer structure in theembodiment shown in FIG. 29. FIG. 36 is a drawing schematically showinga cross-sectional configuration of a photodiode array according to amodification example of the layer structure in the embodiment shown inFIG. 30. FIG. 37 is a drawing schematically showing a cross-sectionalconfiguration of a photodiode array according to a modification exampleof the layer structure in the embodiment shown in FIG. 31. FIG. 38 is adrawing schematically showing a cross-sectional configuration of aphotodiode array according to a modification example of the layerstructure in the embodiment shown in FIG. 32. The basic planarconfiguration and connection relation of these are the same as thoseshown in FIG. 25.

In the structures shown in FIGS. 33 to 38, as described above, an n-typesemiconductor layer R33 or R35 is used instead of the p-typesemiconductor layer 33 or p-type semiconductor layer 35 in FIGS. 26, 28,29, 30, 31, and 32. In this case, the pn junctions are formed at theinterface between the low-concentration n-type semiconductor layer R33(or R35) and the p-type semiconductor regions 34, depleted layers spreadfrom the pn junctions toward the n-type semiconductor layer R33 (orR35), and, corresponding to the depleted layers, the multiplicationregions AM are formed from the pn junction interfaces toward the n-typesemiconductor layer R33 (or R35). The other structure and action are thesame as those as described above.

These photodiode arrays PDA1-PDA4 are configured so that the pluralityof photodetecting channels CH for the detection target light to beentered thereinto are formed on the n-type substrate 22 having then-type semiconductor layer 32. They are the photodiode arrays whereinthe plurality of photodetecting channels CH for the detection targetlight to be entered thereinto are formed on the substrate having the n⁺type semiconductor layer 32 (S) of the first conductivity type. Theplurality of photodetecting channels CH are provided with the substrate22, the n⁻ type epitaxial semiconductor layer R33 (or R35) of the firstconductivity type, the p⁺ type semiconductor regions 34 of the secondconductivity type, and the plurality of resistors 24. The epitaxialsemiconductor layer R33 (or R35) is formed on the first conductivitytype semiconductor layer 32 of the substrate 22. The epitaxialsemiconductor layer R33 (or R35) has the plurality of multiplicationregions AM for avalanche multiplication of carriers generated withincidence of the detection target light, so that the multiplicationregions AM correspond to the respective photodetecting channels. Thesemiconductor regions 34 are formed in the epitaxial semiconductor layerR33 (or R35) to form the pn junctions at the interface to the epitaxialsemiconductor layer R33 (or R35). The plurality of resistors 24 eachhave the two end portions and are provided for the respectivephotodetecting channels CH. The plurality of resistors 24 each areelectrically connected through the one end portion 24 a to the secondconductivity type semiconductor region 34 in the epitaxial semiconductorlayer R33 (or R35) and are connected through the other end portion 24 bto the signal conducting wire 23.

The resistors 24, as shown in FIG. 25, are provided for the respectivephotodetecting channels CH through the one end portion 24 a and channelperipheral portion 23 c and are connected each through the other endportion 24 b and connecting portion 23 b to the readout portion 23 a.The plurality of resistors 24 to be connected to the same readoutportion 23 a are connected to the readout portion 23 a.

In these photodiode arrays, the pn junctions are composed of theepitaxial semiconductor layer R33 (or R35) of the first conductivitytype on the substrate and the semiconductor regions 34 of the secondconductivity type formed in the epitaxial semiconductor layer R33 (orR35). The multiplication regions AM are formed in the epitaxialsemiconductor layer R33 (or R35) where the pn junctions aresubstantialized, and the multiplication regions AM corresponding to therespective photodetecting channels are present in the epitaxialsemiconductor layer R33 (or R35).

INDUSTRIAL APPLICABILITY

The present invention is applicable to semiconductor photodetectionelements and photodetection apparatus.

LIST OF REFERENCE SIGNS

-   -   1 n⁻ type semiconductor substrate; 1 a first principal surface;        1 b second principal surface; 3 p⁺ type semiconductor region; 5        n⁺ semiconductor region: 10 irregular asperity; 11 accumulation        layer; 13, 15 electrodes; 22 substrate; 23 signal conducting        wires; 24 resistors; 25 electrode pad; 31 insulating film; 32 n⁺        type semiconductor layer; 33 p⁻ type semiconductor layer; 34 p⁺        type semiconductor regions; 35 p-type semiconductor layer; 36        protecting film; 40 separating portion; 42 light shielding        portion; AM multiplication regions; CH photodetecting channels;        S substrate member; PL pulsed laser beam; PD1-PD4 photodiodes;        PDA1-PDA4 photodiode arrays.

The invention claimed is:
 1. A front-illuminated type photodiode arrayin which a plurality of photodetecting channels configured for detectiontarget light to enter thereinto are formed on a silicon substrate havinga semiconductor layer of a first conductivity type, the photodiode arraycomprising: an epitaxial semiconductor layer of a second conductivitytype formed on the semiconductor layer of the first conductivity type,forming pn junctions at an interface of the semiconductor layer, andhaving a plurality of multiplication regions for avalanchemultiplication of carriers generated with incidence of said detectiontarget light, so that the multiplication regions correspond to therespective photodetecting channels; and a plurality of resistors eachhaving two end portions, provided for the respective photodetectingchannels, and each electrically connected through one of the endportions to the epitaxial semiconductor layer and connected through theother of the end portions to a signal conducting wire, wherein anirregular asperity is formed in at least a surface corresponding to thephotodetecting channels in the semiconductor layer of the firstconductivity type, wherein at least the surface corresponding to thephotodetecting channels in the semiconductor layer of the firstconductivity type is optically exposed, and wherein a surface opposed tothe surface with the irregular asperity formed therein constitutes alight incident surface, light incident from the light incident surfacetravels in the silicon substrate.
 2. The front-illuminated typephotodiode array according to claim 1, wherein the irregular asperity isfurther formed in a surface corresponding to a region between theplurality of photodetecting channels in the semiconductor layer of thefirst conductivity type and the surface is optically exposed.
 3. Thefront-illuminated type photodiode array according to claim 1, wherein inthe silicon substrate, a portion where the plurality of photodetectingchannels are formed is thinned while leaving a surrounding region aroundsaid thinned portion.
 4. The front-illuminated type photodiode arrayaccording to claim 1, wherein a thickness of the semiconductor layer ofthe first conductivity type is larger than a height difference of theirregular asperity.
 5. The front-illuminated type photodiode arrayaccording to claim 1, wherein the light incident from the light incidentsurface and traveling in the silicon substrate is reflected, scattered,or diffused by the irregular asperity.